diff --git a/tests/test-check-release-needed.sh b/tests/test-check-release-needed.sh
index 75d15e2..440960b 100755
--- a/tests/test-check-release-needed.sh
+++ b/tests/test-check-release-needed.sh
@@ -76,12 +76,21 @@ EOF
 # $3 is optional: pre-commit's PRE_COMMIT_TO_REF, the local sha being pushed.
 # Left off entirely, the variable stays unset and the script falls back to HEAD,
 # exactly as a plain `git push <remote> <current-branch>` behaves.
+# The fixture repo is the subject under test, so every PRE_COMMIT_* input must
+# come from this function and nowhere else. Any such variable already in the
+# environment belongs to the *caller's* repo: run under the pre-push hook this
+# suite guards, PRE_COMMIT_TO_REF holds a sha of the real repo, which does not
+# exist in the fixture, and the script resolves against the wrong rev. Clearing
+# them is what makes a standalone run and a pre-push run the same test — this
+# suite passed everywhere except under the hook it exists to protect.
 run_check() {
   local dir="$1" branch="$2"
   if [[ $# -ge 3 ]]; then
-    (cd "$dir" && PRE_COMMIT_REMOTE_BRANCH="$branch" PRE_COMMIT_TO_REF="$3" bash "$SCRIPT" 2>&1)
+    (cd "$dir" && unset PRE_COMMIT_FROM_REF \
+      && PRE_COMMIT_REMOTE_BRANCH="$branch" PRE_COMMIT_TO_REF="$3" bash "$SCRIPT" 2>&1)
   else
-    (cd "$dir" && PRE_COMMIT_REMOTE_BRANCH="$branch" bash "$SCRIPT" 2>&1)
+    (cd "$dir" && unset PRE_COMMIT_FROM_REF PRE_COMMIT_TO_REF \
+      && PRE_COMMIT_REMOTE_BRANCH="$branch" bash "$SCRIPT" 2>&1)
   fi
 }